Wow, I wasted all this argument on a slipknot thread. I really don't feel like trying to prove that art isn't subjective again, especially since people tend to be so rigid that they can't change their minds, and you can waste hours on stuff like that. Just look at it this way. My dad is getting a masters of fine art degree. One day, he came home proclaiming that there is no such thing as good and bad and that the concepts of good and bad are merely social constructs. About a month later, he was back to dissing the bad shit and praising the good. I noticed, but I think he had completly forgotten that art is subjective crap. Look at it this way, are the words I am typing equal to poetry? No freaking way. People put a ton of time into shit like that. Quality is a product of work and skill. There is no way that a recorded belch is equal to Hvis Lyset Tar Oss, and to deny it makes you clueless, unless you can show that the recorded belch was the result of the invention of the recorder or something. Sure, some postmodern theorist may agree with you, but your definition of art is not what would be generally agreed upon. When people see good art, they want something that commands respect. They want to see the outcome of dedication and hard work, not some half-assed job.
Now, to progress to the genres debate. Don't diss genres. Or more specifically, don't say all X is bad. Not all metalcore sucks. I guess you could say nu-metal sucks. As long as you don't imply that every nu-metal band sucks. Nu-metal is a bad genre, I suppose. But, there is good nu-metal. There is good country (Johhny cash, neil young), good rap (a tribe called quest), good techno (kraftwerk), and good whatever you can think of.